Identification and informed consent A cohort of pregnant women (in their third trimester) would be identified through the baseline census and subsequent updates during the surveillance period. The investigators will then identify births within 24 hours of birth through an information system employing the assistance of Lady Health Workers (LHWs) of the area and the traditional birth attendants (TBAs). Families will be visited prior to birth to sensitize them about the study and provide an information sheet. Following notification of births, the families will be visited again and informed consent sought prior to initial randomization. The recruited infants and families will be visited, 3 times per week to assess morbidity and growth (height, weight, mid-arm circumference and head circumference). Close liaison would be maintained with the local vaccination centers, where the OPV doses would be administered to the infants according to the EPI schedule of Immunization. Efforts would be made by the research staff to maintain a record of all vaccinations of the recruited cohort, along with dates for subsequent vaccinations.